In DE 101 33 384 A1 a particle sensor is described, in which the electrodes are interlocked with one another in an alternating comb-like manner and which can be termed interdigital-electrodes. The impedance and/or its variation between the two electrodes can at least be used as a measure for the particle mass, which occurred in a preset time and/or related to the driving distance a of a motor vehicle, in which a combustion engine is used as a drive. Because the measuring effect is based on an accumulation of particles, the particle sensor can be termed collecting particle sensor.
DE 10 2005 034 247 A1 describes a procedure for controlling an exhaust gas threshold value of a combustion engine by use of a controller, which evaluates the signal of at least one exhaust gas sensor and provides an error signal if an exhaust gas threshold value is exceeded. Thereby the emission of the combustion engine that has been calculated for the present driving status is detected by use of a model of the combustion engine and compared to the signal of the exhaust gas sensor or a reference value that has been deduced from it. The exhaust gas sensor can be a particle sensor that is arranged downstream after the particle filter. For evaluating, if the particle filter is defect, the quotient of the measure for the particle current, which has been determined by the particle sensor, and of the calculated particle emission is build and compared to a threshold value.
DE 10 2006 018 956 A1 describes a procedure for determining a particle mass or a particle mass current in a flue of a combustion engine by use of a particle sensor, whereby the detected signal variation is compared to an anticipated signal variation that has been calculated by use of a combustion engine model. Thereby it is provided that the detected signal variation of the particle sensor and/or the calculated anticipated signal variation of the particle sensor are corrected considering the influence factors on the cross sensitivity of the particle sensor. Therefore the efficiency of the particle filter can be determined comparably exactly with the pre-known procedure even during dynamic processes.
A collecting particle sensor collects not only the particles that have to be detected, but also the ash that is contained in the exhaust gas. While the particles that have to be detected can be eliminated within a regeneration by heating the section of measurements of the particle sensor up to a free-burn temperature, the ash that has condensed on the section of measurements cannot be eliminated offhand. But also on the section of measurements of a non-collecting particle sensor an ash condensation can occur, which affects the measuring signal. Due to the ash contamination the remaining operating time of the particle sensor is limited to a value, at which the sensitivity towards the particles that have to be detected falls under a preset measure.
The invention is based on the task, to provide a procedure for operating a particle sensor that is arranged downstream after a particle sensor and a device for implementing this procedure, with which the particle sensor can be operated as long as possible despite the impact of ash, which can occur especially at a defect of the particle filter.
This task is solved by the specified characteristics in the independent claims.